This is going to be long winded since I travel quite a bit by plane now, (at least every other week). Experiences will vary between airports and where you are traveling. My experiences are between O'hare (Chicago) and East and South of Chicago. Your experiences will also very depending on the time of year, and the security state at your airports.
I would like to say, I never ever tell them I have a pump until I get questioned. Why create a delay or a pat down? There is absolutely no reason to tell anyone about a medical condition. I'm vocal with my friends and family that I have diabetes, and that I have a cool pump - but I'm not going to tell some stranger the same information.
You should know there are 2 different types of body scanners for all airports. Millimeter wave scanners (you walk into a tube) & background (x-ray) scanners. (Stand between 2 panels) Thought he pump companies say "Do not X-Ray" - I never take my pump off and put it though the bag scanner, but I see little risk to the body scanners. Again your choice - I'm not advocating any way you want to choose going through security. If something jacks my pump up, I always have pens and an insurance policy that will replace my pump.
Metal detectors at all airports are different. If there is no scanner at your security station, you will go through the doorway of "Ding" (LOL) most times even if there is a body scanner. I've had about a 50/50 chance the pump was not detected. If you ping the detectors, just pull the pump out and show them, you will need the pat down. No ding - go straight through and no worries.
O'Hare is interesting. Body scanners. I've flown both American & United (2 different terminals) and to tell you the truth, United is the fastest. They seem to understand what a pump is. American, I always get a hassle. I think I can only remember once where I was not patted down after going through the body scanner. The pat downs are fast. It only adds maybe 5 to 10 minutes of extra time - and to be honest, I've never been treated bad at O'Hare. Body scanners will always see the pump and tube. Again, just pull the pump out and show them.
Laguardia (NY) (no body scanners) & Newark (NJ) (body scanners) were fast as well. Laguardia doesn't have body scanners (as of today). Laguardia I've never had an extended pat down, and I've never pinged the metal detector. Fastest airport ever. Newark is not fast. Expect to walk through a 45 minute line each and every time. Pat down at Newark is fast, and not cumbersome. Newark also offers a liquid testing program (new at some airports) where you can bring more then 4 oz of liquids through. I've not used this option, so take that at your own risk.
Boston - UGH. can I say UGH again? This was a crappy experience. I've only flown through here once, and it was right before Christmas, so a high security time. Body scanner. I was fully patted down, questioned to death and had both my bags inspected. It took an additional 30 minutes. I was questioned about all my medications. I will be going back through Boston next week, so if I have the same experience, I'm going to try and avoid this airport if I have a choice.
Nashville (body scanner) - all I can say is AWESOME. These people had their stuff together. Again, I still had to have a pat down, I had forgotten a soda in my bag, because I was late to the airport. They let me keep it! They had a liquid testing station there, though it was not advertised like Newark.
As I say this, your millage may very depending on your attitude and the attitude of the TSA agents. I'm always polite, I'm always up front about my pump (after being asked). Most TSA agents are professionals (ya I said that) just doing a job.
If you have any other questions - feel free to PM me - I think this post is long enough.